1. Field of the Invention
This invention relates to a chip inductor of the type having terminal electrodes formed on the surface of a magnetic core.
2. Description of the Prior Art
FIG. 5 is a perspective view showing an example of a conventional chip inductor. It comprises a magnetic core 2 made from ferrite or the like having a winding support portion 2a and flange portions 2b and 2c formed on the upper and lower sides of said winding support portion 2a, a winding 4 mounted on said winding support portion 2a, a pair of terminal electrodes 6a and 6b for installing said inductor on a printed circuit board or the like, the opposite ends of said winding 4 being electrically connected to the terminal electrodes 6a and 6b as by soldering (not shown).
Silver-palladium (Ag-Pd) has heretofore been used for said terminal electrodes 6a and 6b to provide protection against the electrode material being leached by soldering. Although such solder leaching can be minimized by increasing the palladium content, adhesion to solder decreases. Further, since palladium is expensive, there has been a need for some other metal which is less expensive.
As an approach thereto, the use of nickel, which is most effective for prevention of solder leaching and which is inexpensive, for the terminal electrodes 6a and 6b, would be contemplated; however, since nickel has a relatively low resistance and a relatively high magnetic permeability, the use of nickel for said terminal electrodes 6a and 6b would offer a problem that the Q factor of the inductor is deteriorated to a large extent by eddy current loss produced therein.
More specifically, the magnetic flux produced in the winding 4 also necessarily passes through the terminal electrodes 6a and 6b, whereupon an eddy current flows in the terminal electrodes 6a and 6b. This eddy current i is generally expressed by rot i=-k (dB/dt), where k is conductivity, which is the reciprocal of resistivity, and B is magnetic flux density. In this case, the higher the magnetic permeability of the terminal electrodes 6a and 6b, the greater the amount of magnetic flux passing therethrough and hence the greater the magnetic flux density B. Further, the smaller the resistivity, the greater the conductivity k and hence the eddy current i increases, producing energy loss which, in turn, results in a high deterioration in the Q factor.